1. Field of the Invention
The present invention relates to a surface acoustic wave device having surface acoustic wave elements face-down mounted in a package and, more particularly, to a surface acoustic wave device having a plurality of surface acoustic wave elements mounted side by side in one package and a method of manufacturing the same.
2. Description of the Related Art
Prior Art
Recently, to cope with international roaming services (e.g., roaming services based on the US-CDMA scheme and JAPAN-CDMA scheme) in the field of mobile communication, a surface acoustic wave device in a single package which can cope with a plurality of communication schemes has been developed. As a means for implementing such a package, a method of mounting a plurality of surface acoustic wave elements having different frequency characteristics in correspondence with different communication schemes in a common package (to be briefly referred to as a multichip package hereinafter) is available.
As a method of mounting each surface acoustic wave device in a package, the face-down bonding scheme has been developed and put into practice, which can further reduce the device size as compared with the conventional wire bonding scheme.
In applying the face-down bonding scheme to a multichip package, first of all, the first element is face-down mounted on the base of a package, and the connection terminals of a surface acoustic wave comb electrode are joined to a metalized layer formed on the inner surface of the base (die attach surface) through metal bumps serving as joining or bonding members. The second element is then mounted in a space adjacent to this element, and joined or bonded to the metalized layer of the package through metal bumps in the same manner as described above. In this joining/bonding process, a load is imposed from a tool holding the element to the metal bumps, and at the same time, ultrasound waves are applied to the metal bumps through the tool. As a consequence, the metal bumps melt to join or bond the electrode connection terminals to the metalized layer.
For example, a conventional multichip surface acoustic wave device is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-122072 (see FIG. 1 of this publication). The device in this reference uses the above xe2x80x9cface-down bonding schemexe2x80x9d.
Problem
In the joining/bonding process, since ultrasound vibrations are applied to the holding tool, a surface acoustic wave element is mounted with a positional shift. When the second element is inserted into the package, it (the second element) comes into contact with the first element or a side wall of the package, causing an inconvenience related to the degree of positional shift. For this reason, an adequate (large) margin must be provided in advance for the mount position of each element.
As the above (large) margin is provided, it becomes more difficult to attain a reduction in device size. Demands have therefore arisen for further improvements.
Object
The present invention has been made in consideration of the above situation and, has as its object to provide a multichip package surface acoustic wave device and a method of manufacturing the device, which can attain a reduction in device size as compared to the conventional device.
In order to achieve the above object, in a method of manufacturing a surface acoustic wave device according to an aspect of the present invention, in the step of joining or bonding the electrode terminals of a surface acoustic wave element to the die attach surface of a package, the ultrasound wave application direction is set to a direction substantially perpendicular to the element layout direction.
The positional shift of a surface acoustic wave element increases along the ultrasound wave application direction. By setting this ultrasound wave application direction to a direction in which no other chip (no other surface acoustic wave element) is mounted, the margin of a mount position can be greatly reduced (to almost xc2xd) as compared with the case where the ultrasound wave application direction is set to the chip mounting direction. This makes it possible to reduce the size of a surface acoustic wave device.
A surface acoustic wave device according to another aspect of the present invention is configured such that each metal bump has a smashed shape whose major axis coincides with a direction substantially perpendicular to the direction in which a plurality of surface acoustic wave elements are juxtaposed (shape 14 elongated in the vertical direction in FIG. 4).
By making the application direction of ultrasound waves or the like in the joining/bonding step substantially perpendicular to the element juxtaposition direction, each metal bump has a shape smashed along the ultrasound wave application direction in the joining/bonding step. If each connection terminal of a comb electrode is formed into an elongated shape in accordance with the smashed shape of this metal bump, the area occupied by the connection terminal can be reduced while an adequate bonding strength/bonding area is ensured. This makes it possible to attain a reduction in package size.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.